1. Field of the Invention
This invention relates to a semiconductor packaging structure in which lead frame conductors used to plug a semiconductor structure into a socket or pc board extend over and are adhesively joined to the surface of the chip via an insulated conductive ground plane structure positioned between the lead frame and the chip surface and electrically connected to a respective lead frame conductor. The remainder of the lead frame conductors may be electrically connected to respective terminals on the semiconductor chip surface.
2. Description of the Prior Art
U.S. Pat. No. 4,862,245 assigned to the same assignee as the present invention, describes a technique for positioning and affixing leads to a semiconductor chip prior to encapsulation of the chip in a protective coating by extending the lead frame over the surface of the chip.
A common problem with the prior art semiconductor package occurs when the lead frame becomes highly packed and when the underlying semiconductor device is a so-called high performance device in which a signal frequency is in the sub-nanosecond range, in such devices the noise level can rise above the signal levels and signals can become lost and the heat generated by the device can be significantly increased. This noise to signal ratio and increase in generated heat effectively limits the use of these devices when they are packaged as taught in the referenced patent.
It is an object of this invention to provide a packaged semiconductor chip with improved electrical and thermal performance.
Still another object of the invention is to provide a packaged semiconductor chip in which noise levels are maintained below the signal levels of the chip when it is operating at a sub-nanosecond signal transfer rate.
It is a further object of the invention to provide a packaged semiconductor chip which has reduced cross-talk.
It is still a further object of the invention to provide a packaged semiconductor chip which as improved heat transfer characteristics.
It is still another object of the invention to provide a plastic encapsulated semiconductor package in which the connecting lead frame members are deposited over the surface of the device together with a covering ground plane so as to provide enhanced electrical and thermal coupling of the members and the device and so reduce the signal to noise ratio by a factor of greater than three over that available in other similar plastic encapsulated packages while simultaneously improving the transfer of heat out of the package.
These and other objects of the present invention are provided by attaching a lead frame, having a plurality of conductors, to a major active surface of a semiconductor chip via a ground plane. In the preferred embodiment, a multilayered structure containing an insulated integral, uniform ground plane is positioned between the lead frame and the chip and is adhesively and insulatively joined to both of them. As will be described later different adhesives may be used to attached the interposer to the chip and to the lead frame Wires connect terminals on the major active surface of the semiconductor chip to the ground plane and to selective lead frame conductors. The lead frame, the ground plane structure, the semiconductor chip, and the wires which connect the semiconductor chip terminals to the ground plane and to selected lead frame conductors are encapsulated with a suitable insulating material to form a semiconductor module or package.
A bus bar can be provided that extends along the entire length of the semiconductor chip to serve both as a ground bus and as a means for further dissipating heat generated by the chip. This bus bar is connected to the integral ground plane structure as well as to selected terminals on the semiconductor chip.
These and other objects, features and advantages of the invention will becomes more apparent from the following particular description of the preferred embodiment of the invention as illustrated in the accompanying drawings.